Bleed air from aircraft engines is commonly used to power hydraulic pumps utilized in aircraft subsystems, and especially for landing gear and flap hydraulic systems. Such pumps offer reliable, but inefficient, power transfer from bleed air into hydraulic flow and pressure. Expansion of bleed air through a turbine is limited to efficiencies between 50 to 70 percent, depending upon the bleed pressure available.
As aircraft engine designers have sought greater fuel efficiencies, engines have shifted towards higher compression ratios and higher fan bypass ratios to make the engines more fuel-efficient. However, such engines are more sensitive to bleeding air for aircraft subsystems. Thus, new airplane designs with advanced high bypass ratio engines cannot provide traditional support for engine bleed air extraction to power subsystems without a significant efficiency penalty.
This has led to the increased use of electric motor driven subsystems, often with separate motor drives. Different aircraft subsystems, including and commonly hydraulic systems and air conditioning systems, have different power requirements, with power needed in different locations of the aircraft, at different times during the flight and on the ground. Often, due to the constraints of the subsystems, different speeds and torque are required. Multiple electric motor driven subsystems provide flexibility as to location, timing of operation, and velocity. However, for aircraft, multiple electric motor driven subsystems carry the detriment of increased weight.
Therefore, an unmet need exists for drive systems for auxiliary subsystems which reduce weight and size of subsystem drives, while allowing flexible power applicability and flexible rotational velocities for the different subsystems.